1. Field of the Invention
Embodiments of the invention relate in general to seismic surveying using deployable cables containing transducers/sensors for the sensing of received acoustic signals at subsea locations resulting from a generated seismic signal. More particularly, embodiments relate to a device and a method for storing and handling a seismic cable incorporating a number of seismic stations for use in seismic surveying at offshore locations. Operations related to deployment and retrieval of such cables are generally aimed at placing a seismic cable on the sea bottom, normally in a trench, under different weather conditions, and with a failure rate as low as possible.
2. Description of the Related Art
Installation of subsea cables is now a common procedure performed by a number of operators, often using purpose-built or purpose-equipped vessels. U.S. Pat. Nos. 5,624,207 and 5,655,753 to Berges, et al. describe an ocean bottom cable handling system and method of using the system where the cable is stored in large storage bins onboard a vessel.
Typically, such subsea cables are very long and consist of a small number of discontinuities, e.g. regenerators. When repeaters are included along the cable, such repeaters usually requires special handling, such as e.g. hand carrying, in the deployment apparatus onboard a vessel, in order to ensure that no damage is made to the repeaters.
A typical procedure for the installation of a seismic cable involves the handling of a long cable, interrupted by many sensor stations. U.S. Pat. No. 6,070,857 describes a device for the storage and deployment of ocean bottom seismic cable on a vessel comprising a rack on which the long length of seismic cable is suspended prior to deployment into the sea.
U.S. Pat. No. 4,647,253 describes a large capacity, cable turntable assembly for use in connection with laying long lengths of underwater cable. The turntable may be positioned on a shore side support, permitting rotation of the turntable in order to load the cable onto the turntable. The turntable may then be moved laterally onto a support surface on a floating platform, such as a barge.
United States Patent Application Publication No. US 2003/0159877 A1, to Martin, et al., describes a method of performing a seismic survey of a hydrocarbon reservoir at an offshore location where a seismic cable is deployed into a lined trench on the seabed. The cable is deployed from a drum on a remotely operated vehicle.
United States Patent Application Publication No. US 2004/0065443 A1, to Berg, et al., describes an apparatus and method for transporting, deploying, and retrieving an array of a plurality of nodes interconnected by sections of cable. An apparatus and a method for transporting, deploying and retrieving a preassembled fiber optic in-well seismic array having a plurality of fiber optic sensors, clamp mechanisms, and sections of cables between sensors is described.
As described in published United States Patent Application No. US 2004/0065443 A1, difficulties are encountered when the sections of cable and the nodes are wound on to or unwound from a cable drum or other carrying device, due to the size, shape and construction of the nodes. Typically, the nodes constitute bulges on a cable, and the nodes are typically less flexible than the other sections of a seismic cable.
A further limitation of present solutions for seismic cable storage, deployment and retrieval is that a heavy and long cable has a tendency to move and unwind from the drum. Also, if there are a number of seismic stations on a seismic cable, the cable may easily become trapped between other layers of cable or behind seismic stations and an entangled cable may result in kinks or even eventual breakage of the cable.
Deployment and retrieval of seismic cables which include a large number of sensor points or sensor stations with interconnecting cable is presently a challenge for most installation companies.
There exists a need for an improved storage and installation device for use in a cable deployment and retrieval system which may facilitate a more efficient and predictable deployment and retrieval of seismic cables and a method which enables improved functionality while reducing the above mentioned limitation of present solutions.